The only assistant coaching tandem that Peyton Manning has ever known in the NFL is on the verge of a break-up because of a recent change in the league's pension program for non-playing personnel.

Offensive line coach Howard Mudd has informed the Colts he is planning to retire immediately because of the pension-plan changes, according to team and league sources.

"It's a dilemma we're trying to work through," said Bill Polian, the team's president and general manager. "I don't think Howard has turned in his [retirement] papers yet but it's a difficult situation and a very personal choice for Howard."

Mudd has served as the Colts line coach for 12 years with Tom Moore as offensive coordinator under two head coaches, Jim Mora and Tony Dungy, who retired in January. Manning has been the quarterback for 11 of those 12 years, having been drafted a year after they arrived in Indianapolis, and has credited the Moore/Mudd pairing as vital to both the team's success and his own elite status.

The Colts have allowed the fewest sacks during Mudd's 12 seasons, with just 218 sacks allowed in 182 games, including just 14 in 585 pass attempts in 2008.

Mudd could not be reached for comment, but sources indicated it is almost a certainty that he is stepping down and that assistant line coach Pete Metzelaars will assume his duties.

During the league's meetings in March, owners passed a resolution to revise its pension program for non-players.

Mudd, 67, believes he has to take his entire lump-sum pension payment now because if he does not exercise that right at 65 under the revised plan, he will be allowed only to accept annuity payments upon retirement that will be reduced to 50 percent value for his immediate survivors if he dies, according to sources.

Mudd has already maximized his pension because he has surpassed the formula that requires a coach's age and league tenure to equal 75. He has been an NFL assistant for 36 consecutive seasons.

Many assistant coaches are upset with the recent pension revisions and have complained the new program not only reduces their retirement income but also lacks clarity.

There are other long-tenured coaches older than 65 in the NFL who face the same dilemma, including the 70-year-old Moore, who was also unavailable for comment.

A league source said there were several factors that motivated owners to change the pension program, including a loophole that enabled a tenured assistant coach who hit the 75 formula to retire and take a lump sum only to return to a team as a high-paid consultant.